Pupil measurement using the Colvard pupillometer and a standard pupil card with a cobalt blue filter penlight.

Chaglasian EL, Akbar S, Probst LE.

Excerpt:

Chaidaroon and Juwattanasomran conclude that night-vision disturbances are often preventable, especially if patients with higher amount of myopia are accurately identified as having a large scotopic pupil. Newer wavefront technologies demonstrate that spherical and coma aberrations increase with increasing pupil size. Smaller pupils are associated with improved visual acuity in patients after refractive surgery and in untreated patients. Night-vision disturbances have been reported in 25% of 35% of patients after photorefractive keratectomy (PRK) and LASIK using a 6.0 mm ablation zone and in 65.6% of patients treated with a 5.0 mm ablation zone in PRK.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE: To prospectively compare the scotopic pupil size between emmetropes and myopes using a Colvard pupillometer.

METHODS: The pupil diameters of 55 normal subjects and 55 healthy myopic subjects were measured with the Colvard pupillometer in a low-light situation that simulated the level of light encountered while driving at night.

RESULTS: The mean (+/- SD) age of the emmetropic subjects was 30.78 years +/- 10.03 (range, 18-54 years) and the mean (+/- SD) age of the myopic subjects was 27.35 years +/- 8.43 (range, 21-52 years). The mean (+/- SD) scotopic pupil diameter was 6.46 +/- 0.90 mm (range, 4.5-8.0 mm) in the emmetropic group and 6.98 +/- 0.67 mm (5.5-8.5 mm) in the myopic group. The unpaired Student t-test showed that the difference in the scotopic pupil diameter between emmetropes and myopes was statistically significant (P =.0001).

CONCLUSIONS: The mean scotopic pupil diameter in myopes was larger than that in emmetropes. Therefore, a large ablation zone of the cornea or an appropriate optical size of the phakic intraocular lens should be considered in refractive surgery. Preoperative scotopic pupil measurements may be necessary in all refractive patients.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

A series of 85 patients with myopia, up to -6.00D, was treated by photorefractive keratectomy (PRK), using a 5 mm diameter ablation zone. At six months, 38 patients (45%) reported slight disturbances of night vision, nine (11%) of whom had significant problems. Perturbations of night vision after PRK are seen as starbursts and halos around lights. Corneal haze produces the starbursts, which are usually transient. In contrast, halos are myopic blur circles and may be persistent. Using a computer program, halos after PRK were found to be significantly larger than those in emmetropes and myopes corrected with spectacles (p < 0.01). The halos were diminished by using either artificial pupils or negative lens over-correction. In patients with identical bilateral PRK corrections, except for the ablation zone size, the magnitude of the halo was less with 5 mm than 4 mm zones (p < 0.01). Patients treated with 5 mm reported fewer problems attributable to halo than with the 4 mm ablation diameters (p < 0.01). Halos and pupil diameters were measured in nine patients with significant impairment of night vision haze. Those with starbursts had small hyperopic shifts, minimal halos and high haze and light scatter measurements, whilst patients with halos had large hyperopic shifts, little haze and large pupil diameters. Patients with persistent halo problems benefited from either negative lens over-correction or miotics at night.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Comparison of the pupil card and pupillometer in measuring pupil size.

Pop M, Payette Y, Santoriello E.

Michel Pop Clinics, Montreal, Quebec, Canada.

PURPOSE: To determine the difference in pupil size measured with the Colvard pupillometer in mesopic and scotopic luminance and with the Rosenbaum pupil card in mesopic luminance between 2 examiners.

SETTING: Michel Pop Clinics, Montreal, Quebec, Canada.

METHODS: Two examiners used the Colvard pupillometer and the Rosenbaum card to measure pupil size in 58 eyes. The Colvard pupillometer was used in mesopic and scotopic light conditions. The Rosenbaum card was used in mesopic luminance only. Pupil size was evaluated with a 1.0 mm interval scale at the nearest half millimeter.

RESULTS: For the 3 sets of data, the limits of agreement and coefficient of interrater repeatability were calculated and a 2 x 2 factorial analysis of variance was performed. Because of interexaminer bias, measurements done in mesopic luminance with the Rosenbaum card were not statistically different from those with the Colvard pupillometer in scotopic luminance, although interrater repeatability of the Colvard pupillometer (0.8 mm) was superior to that of the Rosenbaum card (1.3 mm).

CONCLUSIONS: Examiner bias was the greatest statistical bias in all sets of measures. Surgeons may want to opt for a "safe" limit of pupil size (ie, 0.5 to 0.8 mm greater than the measured size) when calculating optical zones in refractive surgery. Future devices for pupil measurement should be based on automatic adjustment sizing.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Finally, in data analysis, the pupl size was chosen to be 5.0 mm derived from an ablation zone of 6.0 mm diameter. This essentially limits our conclusions to photopic and mesopic lighting condition. Nevertheless, patients with significantly larger pupils are usually screened out for refractive surgery.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

PURPOSE: To identify factors that affect the change in lower- and higher-order wavefront aberrations after myopic wavefront-guided laser in situ keratomileusis (wg-LASIK). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Sixty myopic eyes of 32 patients were treated with wg-LASIK (Zyoptix version 3.1, Bausch & Lomb) and had an uneventful follow-up of 12 months. Wavefront errors were measured preoperatively and 12 months after LASIK and were computed for pupil diameters (PDs) of 3.5 mm and 6.0 mm. Multiple stepwise regression analysis was performed to assess the influence of patient age, spherical equivalent (SE), sphere, cylinder, optical zone (OZ) diameter, and the preoperative individual Zernike coefficients on lower- and higher-order aberration (HOA) change. RESULTS: The mean preoperative SE was -5.59 diopters (D) +/- 2.20 (SD) (range -1.00 to -9.50 D); the mean OZ diameter was 6.70 +/- 0.68 mm (range 5.6 to 8.1 mm). Reduction in almost all Zernike coefficients was influenced significantly by the preoperative amount of the individual coefficient. The effect varied among the coefficients and was lower with the 6.0 mm PD. With the 3.5 mm PD, age, SE, sphere, cylinder, and OZ diameter did not have a significant effect on individual Zernike coefficients. With the 6.0 mm PD, SE and OZ diameter had a significant effect on the induction of Z4(0); the OZ diameter also had an effect on the induction of coma root mean square. CONCLUSIONS: Three groups of factors influenced the change in HOAs: The negative correlation with the magnitude of preoperative HOA values reflected the effect of the wavefront-guided algorithm. The SE and OZ diameter affected the inadvertent induction of spherical aberrations. Randomly acting effects such as decentration or flap creation, which were not included in the model, affected the induction of HOAs, particularly coma-like terms.

Huynh and coauthors (pages 948?953) describe how a 6.0 mm excimer-laser-treated zone yields a smaller functional optical zone The authors used a ray-tracing method to measure the potentially unfortunate optical consequences in patients whose pupil diameter is wider than the effective optical zone. In describing the phenomenon of a transitional area within the treated zone, they provide another explanation of why treated areas result in smaller functional areas.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Making sense of refractive surgery in 2001: why, when, for whom, and by whom?

Mannis MJ, Segal WA, Darlington JK.

Department of Ophthalmology, University of California Davis, Sacramento, USA.

Surgical alteration of the focusing or refractive properties of the eye has been performed on millions of patients. An array of procedures to correct myopia, hyperopia, astigmatism, and presbyopia have been introduced over the past 25 years with varying degrees of success. Improved technology has increased patient and physician satisfaction and enthusiasm. Currently available surgical procedures can be categorized as incisional, surface-altering, lamellar, and intraocular. The choice of procedure depends on individual patient indications and contraindications based on results of ocular examinations, eg, corneal pachymetry to measure corneal thickness, keratometry to measure the corneal curvature, basal tear secretory rate, and dark-adapted pupil size. The postoperative uncorrected visual acuity depends, in large part, on the quality of the preoperative evaluation and refraction. Before scheduling a patient for surgery, the ophthalmologist must ensure that the patient understands the potential risks of the procedure and has realistic expectations for the postoperative level and quality of uncorrected visual acuity. Postoperative complications include corneal flap displacement, undercorrection and overcorrection, and epithelial ingrowth under the corneal flap and inflammatory keratitis. Postoperative dry eye, infection, and inflammation are usually treated medically. Ongoing technological innovations to customize the surgical approach to an individual patient's eye continue to improve outcomes.

"Determination of pupil size in a darkened room is essential in the preoperative evaluation to identify patients who may be at risk of glare and halos after surgery. Patients with dark-adapted large pupils should be warned of the higher risk of postoperative visual distortion or glare in dark illumination."

"Medical contraindications to LASIK include a cornea that is too thin or eyes with corneal ectasia in association with irregular astigmatism. Ocular disease, including active collagen vascular disease, rheumatoid arthritis, central panstromal corneal scars, and active herpetic keratitis, contraindicates LASIK in most instances. Relative contraindications are moderate to severe dry eye, cataracts, severe diabetes, advanced or unstable glaucoma, severe anterior basement membrane dystrophy, and pupil size greater than the maximum available ablation optical zone of the laser to be used."

Several vision changes have been described following LASIK, including halos, glare, and ghosting of images. These visual changes occur most often in patients who have pupils that are larger than the ablation zone.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Infrared pupillography is an exact but laborious method for measuring pupil diameter. However, this method was chosen because it has been shown to be more accurate than conventional comparison pupillometry using pupil size charts. Laser in situ keratomileusis creates a different refractive power within the ablation zone than in the peripheral untreated area of the cornea. It is crucial that this zone extends over the maximum optical aperture, defined by the pupil under mesopic conditions. If the measured pupil diameter is greater than the ablation zone, 2 focal points are generated by the cornea (Figure 2). The first one is generated by central light rays refracted by the dioptric power of the ablation zone, calculated for a position located exactly on the retina. The second focal point is generated by the rays passing through the peripheral untreated cornea?in front of the retina in the case of a myopic refractive error and behind it in the case of a hyperopic error. This second focal point creates an out-of-focus image on the retina that overlies the proper retinal image and leads to a halo for the patient.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

Monochromatic wavefront measurements were made using a 6.5-mm aperture of eyes that had programmed optical zone sizes of <6.5 mm, 6.5 mm, and >6.5 mm. They found the measured higher order aberrations to be less in the eyes with larger optical zones. This observation, although important, may or may not be relevant to the visual outcome of the individual patient. Using a fixed aperture of 6.5-mm through which to measure aberrations biases the outcome of the current study.

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A more relevant measure of aberrations than the fixed 6.5-mm aperture used in the study then would be to adjust aperture size according to individual patient pupil diameters under conditions simulating normal daytime and nighttime lighting conditions. In this way, the aberrometer would measure what the patient actually sees.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

The area of the cornea that contributes to the formation of the foveal image is called the optical zone, which covers the entrance pupil. The diameter of the pupil determines the width of the useful optical zone, which varies as a function of the pupillary dynamics.2,3 For a retinal image to constantly have high quality, no aberrations should be present within the entrance pupil under conditions of maximum physiologicalmydriasis.

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If the spherical aberration becomes excessive, a significant loss in contrast transfer and increasing blurring of the images can occur, which can be irritating particularly under conditions of low light intensity when the increase of the pupil diameter causes an increase in the value of spherical aberration.

_________________Broken Eyes

"The price good men pay for indifference to public affairs is to be ruled by evil men." Plato

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